The present application is concerned with improvements in the technique for fiberizing glass or similar thermoplastic materials, especially mineral materials, in which a centrifugal spinner is employed, usually mounted on an upright axis, a stream of glass being fed into the interior of the spinner and being delivered to the inside surface of a peripheral wall of the spinner in which a multiplicity of orifices are provided, so that upon rotation of the spinner, the glass is projected by centrifugal force in streams or "primaries" from the orifices in the peripheral wall of the spinner. Provision is made for delivering an annular stream of attenuating gas in the form of a blast from a combustion chamber, the annular stream being directed downwardly adjacent to the outside surface of the perforate peripheral wall of the spinner, whereby the streams of glass are attenuated and usually also coated with a binder and are then carried downwardly in the attenuating blast to the upper surface of a foraminous collecting conveyor, usually arranged as the bottom wall of a collecting chamber. In a typical installation, suction boxes are disposed below the foraminous collecting conveyor in order to assist in the production of a mat or blanket of the fibers on the conveyor, which blanket is carried away for further treatment, packaging, etc.
In commonly employed systems of this known type, it has been customary to employ so-called "soft" glasses, i.e., glass compositions which are specially formulated to have temperature/viscosity characteristics providing a viscosity which will pass freely through the orifices in the spinner wall at a temperature well within the limits of the temperature which the material of the spinner is capable of withstanding without excessive corrosion and deformation.
For the above purpose, the glass compositions employed have customarily incorporated appreciable quantities of one or more barium, boron, and fluorine compounds, which tend to lower the melting temperature, devitrification of liquidus temperature and the viscosity, and which have therefore been effective in avoiding the necessity for employment of molten glass at excessively high temperatures.
However, the use of compositions containing substantial amounts of boron or fluorine or even barium requires that certain precautions be taken, especially in the case of boron and fluorine because objectionable volatile constituents may be developed and carried through and out of the molten glass production system and, in this event, if this possibility of pollution is to be avoided, special treatment of the discharged gases would be necessary in order to separate and appropriately dispose of those constituents.
Barium, boron and fluorine compounds have heretofore been present in the glasses used, typically in amounts respectively about 3%, 6% and 1.5%, but boron and fluorine compounds commonly employed are volatile at the fusion temperature employed in the glass manufacture and fluorine is even volatile at the temperature employed in fiberization; so that to provide this content of those ingredients requires initial use of larger amounts in the preparation of the glass, because of the losses due to volatilization at glass fusion temperatures.
Still another objection to the employment of substantial quantities of these compounds is the fact that they tend to increase the cost of the fibers being produced. This latter objection is especially so of barium compounds, which are particularly expensive. In addition, the relatively "soft" glasses result in production of glass fibers which are not as highly temperature-resistant as is desirable.
Various factors heretofore encountered in this type of fiberization technique have also tended to limit the production capacity of a given plant facility.